A white light emitting diode (LED) has low power consumption and long lifespan, while not containing toxic heavy metals such as mercury. Therefore, the white LED is being spotlighted as a next-generation artificial light source effective for energy saving and environment protection. Due to such characteristics, the white LED is being quickly put to practical use as a back light unit (BLU) for a liquid crystal display (LCD)-TV, a headlamp for a vehicle, and other general lighting. Demand for the white LED will rapidly increase.
In the present day, the white LED is manufactured mostly by applying yellow phosphor onto a blue LED chip. That is, the above method achieves a white light through combination of a blue light emitted from a blue LED and a yellow light emitted from a phosphor excited by part of the blue light. A representative of the phosphor emitting the yellow light is YAG:Ce3+((Y,Gd)3(Al,Ga)5O12:Ce3+) of Nichia Chemical (Japan), which is known by a high emission efficiency and chemical stability.
Recently, researches are in progress to find a substitute for the yellow phosphor of Nichia Chemical. A phosphor having an oxynitride as a mother body material, such as MSi2O2N2:Eu2+, may be an example of the substitute. The oxynitride-based phosphor is chemically stable and is capable of shifting a light emission wavelength by varying an M ion type and an Eu ion concentration. Accordingly, the oxynitride-based phosphor is attracting attention as a phosphor for the white LED. In addition, the oxynitride-based phosphor has a crystalline structure where M ions and Eu ions are 2-dimensionally (2D) arranged between a 2D layered structure constituted by SiON3 tetrahedrons. Therefore, the oxynitride-based phosphor is expected to show considerably low emission reduction caused due to concentration quenching, in comparison with a phosphor having an 3D arrangement of Eu ions.
In general, the oxynitride-based phosphor is synthesized by a solid phase method that uses solid powder as a raw material. However, the solid phase method is capable of generating a nearly single-phase material only when no Eu or low-concentration Eu is added. When high-concentration Eu is added, that is, when raw materials of Eu (generally, Eu2O3) are increased, content of oxygen may become excessive, thereby easily producing impurities. As a result, the oxynitride-based phosphor may be hardly synthesized in the single phase.